Reference Sand Research Articles

Sustainable utilization of phosphate mine waste rocks as sand substitutes in cement mortar production

The extraction and processing of phosphate ores from sedimentary deposits generates large quantities of mine waste rocks, raising environmental concerns and contributing to landscape disfiguration. This study proposes an eco-friendly approach by exploring the extraction of sand from phosphate waste rocks (PWR) to mitigate the environmental impact associated with the disposal of mine wastes. The investigation focuses on the feasibility of creating masonry cement mortar by incorporating sand obtained from PWR. Three types of sand, Flint (FS), dolomitic limestone (DLS), and phosphate flint (PFS), obtained from the intercalation layers of phosphate were tested as partial replacements for reference sand at varying rates (0 %, 25 %, 50 %, 75 %, and 100 %). The sands were sieved through a 4 mm sieve and characterized to assess their geotechnical, chemical, and mineralogical properties. The toxicity characteristic leaching test analysis was conducted to ensure the environmental safety of recycled sands. Consistent mortar formulations were prepared and cured under uniform conditions. Results showed that a 25 % replacement ratio for each sand type yielded the highest 28-day compressive strengths, exceeding 30.5 MPa. Moreover, the water absorption of mortars decreased from 10.65 % to 8.39 %, 7.29 %, and 5.97 % with the incorporation of 25 % of FS, PFS, and DLS, respectively. Furthermore, toxicity tests revealed that recycled sand met the specified limits for toxic elements Ag, Hg, As, Cd, Cr, Pb, and Zn, and affirmed that incorporating these wastes into MCM significantly reduced the leaching of these metal ions to levels below detection limits (DL=0.01 mg/L). This research contributes to sustainable construction practices by providing a viable solution to minimize mine waste and reduce the construction industry's reliance on natural resources, ultimately addressing both environmental and resource-related challenges.

ASSESSING THE DYNAMIC RESPONSE OF SAND INCORPARATING EXPANDED GLASS GRANULES THROUGH RESONANT COLUMN TEST

In contemporary geotechnical stabilization applications, there is a simultaneous drive to make applications as light and durable as possible while also preferring the utilization of waste products in soil improvement endeavors due to their dual merits of fostering environmental sustainability and conferring economic benefits. In this study, the use of expanded glass granules as a waste material was implemented to harmonize with this perspective, wherein reference sand and expanded glass granules were systematically mixed in varying proportions by mass and volume. Subsequently, the dynamic behavior of the mixture samples was rigorously assessed through a resonant column test between 0.001 - 0.1% shear strain amplitude and under various cell pressures. The variations in modulus reduction and initial shear modulus of the expanded glass granules added specimens were subjected to analysis, the shear modulus values of the samples mass-prepared (1, 2%) were obtained at least 12% and 21% higher than the reference sand, respectively. Similarly, the shear modulus values of the mixture sample prepared at 2.5% by volume were 20% higher than the reference sand at different effective pressures. The specimens prepared at 5% by volume demonstrate shear modulus values that were akin to those of the reference sand. The shear modulus values of the mixture samples prepared by volume (7.5, 10 and 15%) were found to be relatively lower than those of the reference sand. In the experimental study, it was discovered that the high angle of internal friction of the expanded glass granules exerts an influence on the variation in modulus reduction. According to the results of the experimental study, expanded glass granules show positive results in shallow geotechnical soil stabilization applications.

Test conditions influence on thermal conductivity and contact conductance of sand at transient state

The proper assessment of soil thermal properties, such as thermal conductivity, assumes a particular relevance for the design of Ground Source Heat Pump systems, as it determines the heat transfer and the energy efficiency design. Multiple methods can be used for thermal conductivity estimation, however significant scatters in measurements are often reported when using different (or even the same) methods. This work presents a detailed study of the thermal conductivity and the thermal contact conductance of a reference sand tested in transient conditions, analyzing the effect of several factors, such as the heating time, degree of saturation, soil density, temperature and heat flux intensity, on thermal conductivity measurements for dry state or fully saturated conditions. To avoid measurement errors and heterogeneity effects, only three samples were prepared with different compaction ratios, and systematically tested in dry and fully saturated conditions, under different control variables (temperature, testing time, and injected heat flux). Two analytical methods based on the line source solution were used to estimate soil thermal conductivity and to assess the probe-to-soil thermal contact conductance. Significant relationships were obtained between thermal conductivity and soil state conditions and testing variables, highlighting that a heating time longer than the one usually recommended in the standards is clearly needed. Finally, this study uses measured temperature values to determine the probe-to-soil thermal contact conductance, indicating its relevance in soil thermal conductivity estimation.

Effects of initial stress anisotropy on the onset of undrained instability for Guamo sand

Undrained instability is a failure mode that has been observed in many sandy slopes. However, the highly anisotropic stress states caused by the geometry of the slope have not been duly considered from the experimental point of view. This article studies the influence of the initial stress anisotropy of laboratory samples on the static undrained instability of the Colombian reference sand. Forty-five consolidated undrained triaxial tests were performed, prescribing combinations of different initial void ratios, mean confining pressure, and initial stress ratios. Experimental results allow concluding that: a. the size of the instability zone on the p′ − q plane becomes smaller for larger initial anisotropic stress ratios; b. a novel undrained instability plane can be proposed in the p′ − q − e space to set a boundary between stable and unstable undrained loading conditions; c. mean confining pressure plays a vital role in the estimation of undrained instability for Guamo sand samples under low and medium confining stresses; d. despite multiple factors that influence the onset of undrained instability, a relation can be derived between the undrained instability susceptibility of sandy slopes and the initial stress ratio η0.

Concurrent molecular characterization of sand flies and Leishmania parasites by amplicon-based next-generation sequencing

BackgroundPhlebotomine sand flies are vectors of Leishmania parasites, which are the causative agents of leishmaniasis. Herein, we developed an amplicon-based next-generation sequencing (Amp-NGS) to characterize sand flies and Leishmania parasites simultaneously targeting partial fragments of 18S rDNA and ITS1 genes, respectively.MethodsOur assay was optimized using reference sand fly (n = 8) and Leishmania spp. (n = 9) samples and validated using wild-caught sand flies from Palestine. The assay was highly specific, and all DNA references were successfully identified to the species level.ResultsAmong the wild-caught sand flies (n = 187), Phlebotomus spp. represented 95% of the collected samples (177/187), including Ph. sergenti (147/187, 79%), Ph. papatasi (19/187, 10.2%), Ph. perfiliewi (3/187, 1.6%), Ph. tobbi (2/187, 1.2%) and Ph. syriacus (6/187, 3.2%). Sergentomyia spp. represented only 5% (10/187) of the collected samples and included S. dentata (n = 6), S. fallax (n = 2), S. schwetzi (n = 1) and S. ghesquiere (n = 1). The study observed strong positive correlation between sand fly identification results of the Amp-NGS and morphological identification method (r = 0.84, df = 185, P < 0.001). Some discrepancies between the two methods in the identification of closely related species (i.e. Ph. perfiliewi, Ph. tobbi and Ph. syriacus) were observed. Leishmania DNA was detected and identified as L. tropica in 14 samples (14/187, 7.5%).ConclusionsOur assay was sensitive to detect (limit of detection was 0.0016 ng/reaction) and identify Leishmania DNA in sand flies, thus representing a new tool for studying sand flies and their associated Leishmania parasites in endemic areas.Graphical

Using a mixture design method to optimize the behavior of high-performance sand concrete

PurposeThis paper aims to express a mathematical model that predicts the effect of mineral additives on the physical–mechanical properties of high-performance sand concrete (HPSC), using SAS's JMP7 statistical analysis software.Design/methodology/approachA mixture design modeling approach is applied to sand concrete (SC) for optimizing mixtures without being obliged to do a lot of experiments, where the cement is partially replaced with two mineral additives silica fume (SF) and blast furnace slag (BFS) in proportions as high as 20% of the mass. A total of 15 mixtures of sand concrete is prepared in the laboratory using this analytical technique in combinations with binary and ternary systems to estimate the workability and the compressive strength (CS) of sand concrete at 7 and 28 days.FindingsThe results obtained showed that the use of derived models based on the experimental design approach greatly assisted in understanding the interactions between the various parameters of the studied mixtures; the mathematical models present excellent correlation coefficients (R² = 0.96 for CS7 days, R² = 0.93 for CS28 days and R² = 0.95 for slump) for all studied responses. Moreover, it was also found that the inclusion of additives (SF and BFS) in binary mixture SC12 and ternary mixtures SC8 leads to a significant improvement in mechanical strength compared to reference sand concrete SC15. These results give the possibility to obtain a formulation of HPSC.Originality/valueThis paper shows the possibility of manufacturing high-performance sand-concrete with good compressive strength; the developed mathematical model by using SAS's JMP7 statistical analysis software allowed us to reach a strength compression value of about 60 MPa, in 28 days, by replacing 10% of the cement weight with silica fume. Furthermore, with partial replacement of the cement weight (15%) with two additions such as silica fume (10%) and blast furnace slag (5%), a 58 MPa of compressive strength can be achieved, without overlooking the fact that this can be a key economic and environmental alternative.

Screening of reference genes for quantitative real-time PCR in Artemisia argyi

Artemisia Argyi Folium, a traditional Chinese medicine of important medicinal and economic value, sees increasing demand in medicinal and moxibustion product market. Screening stable and reliable reference genes for quantitative real-time PCR(qRT-PCR) is a prerequisite for the analysis of gene expression in Artemisia argyi. In this study, eight commonly used reference genes, Actin, 18s, EF-1α, GAPDH, SAND, PAL, TUA, and TUB, from the transcriptome of A. argyi, were selected as candidate genes. The expression of each gene in different tissues(roots, stems, and leaves) of A. argyi and in leaves of A. argyi after treatment with methyl jasmonate(MeJA) for different time(0, 4, 8, 12 h) was detected by qRT-PCR. Then, geNorm, NormFinder, BestKeeper, ΔCT, and RefFinder were employed to evaluate their expression stability. The results demonstrated that Actin was the most stable reference gene in different tissues and in leaves treated with MeJA, and coming in the second was SAND. Furthermore, the expression of DXS and MCT which are involved in terpenoid backbone biosynthesis was detected in different tissues and after MeJA treatment. The results showed that the expression patterns of DXS and MCT in different tissues and under MeJA treatment calculated with Actin and SAND as internal reference genes were consistent, which validated the screening results. In conclusion, Actin is the most suitable reference gene for the analysis of gene expression in different tissues of A. argyi and after MeJA treatment. This study provides valuable information for gene expression analysis in A. argyi and lays a foundation for further research on molecular mechanism of quality formation of Artemisia Argyi Folium.

Triclosan biodegradation performance of adapted mixed cultures in batch and continuous operating systems at high-concentration levels

Pollutants like triclosan (TCS) of medium to high logKow value tend to be mainly adsorbed and poorly biodegraded during waste water treatment, complicating removal after release. Complete mineralization of TCS is crucial, since transformation products may be even more toxic, but has been proven only in a few cases. In this study, the performance of different batch (cultivation flask, TCSmix100) and continuous operating systems (submerged biotrickling filter, TCSmix100; biomembrane reactor, TCSmix200) was tested with two pre-adapted mixed cultures named TCSmix100 and TCSmix200, and compared to non-adapted cultures in a biotrickling filter and a sand filter as reference systems. Mineralization rates up to 172 mg TCS/L/d were observed during batch conditions for TCSmix100 at 1.45 g TCS/L as initial concentration. Triclosan was completely mineralized by both cultures, as shown by stoichiometric release of chloride at conversion rates of 5,7–11.4 mg TCS/L/d (biotrickling filter) and 0.72–1.45 mg TCS/L/d (biomembrane reactor) at 20 and 7.5–15 mg TCS/L as influent concentrations. In TCSmix100, Achromobacter sp. was identified as the relevant strain in TCS biodegradation. Community analysis of TCSmix200 revealed Nitrosomonas europaea, Nitrospira moscoviensis, Nitrosospira multiformis , and Rhodanobacter lindaniclasticus as the predominant strains. In contrast, chloride formation and triclosan elimination in the non-adapted biotrickling filter was less than 12% of the expected chloride concentration at hydraulic retention times up to 60 d. In the reference sand filter, TCS abatement was 42.8% in average with neither formation of chloride nor increase in biofilm density, indicating mostly sorptive or precipitative effects for elimination. With mineralization levels surpassing those of comparable references by a factor of 3–11, both adapted fixed-biomass reactor systems proved highly suitable for treatment of effluents containing high concentrations of TCS as they occur in industrial discharges or concentrates of membrane-based wastewater treatment plants. • Two aerobic mixed cultures were enriched able to completely mineralize triclosan (TCS) • Mixed cultures were dominated by Achromobacter sp. or nitrifying bacteria • Turnover rates were up to two orders higher than in literature (172 mg TCS L −1 d −1 ) • Fixed biomass systems showed stable performance during 110 d and 137 d of operation • TCS was solely eliminated by sorptive effects in a sand filter as reference system

Study of Head Loss in Rapid Filtration with four River Sands

In this work, we studied the filtration behavior, with regard to the head loss, of four calibrated Togo Rivers sands compared to that of a reference filter sand imported from Europe. The objective is to determine the suitability of local rivers sands as filter sands for water treatment plants. The sands were successively loaded into a filtration pilot and subjected, during at least 20 hours, to the filtration of water whose turbidity was maintained at around 20 NTU. The results show that the average deviations of the head loss profiles as a function of depth, calculated in relation to the head loss recorded on the reference sand, at the same filtration time t=20h, are small and vary from 2 cm to 8 cm. In the same way, the curves of the head loss as a function of time are quite close to the one observed for the reference sand. Examination of the clogging front after 20 hours of filtration reveals that the progression is either the same or greater and reached 20 cm in depth at the same time. This study can be extended to other rivers sand samples and by varying the turbidity and the filtration rate. Doi: 10.28991/cej-2021-03091682 Full Text: PDF

Development of an auto compensation system in cyclic triaxial apparatus for liquefaction analysis

When performing cyclic triaxial tests, the connection process between loading piston and specimen could have significant effect on the test results. Tensile pre-shearing effect occurs during saturation and consolidation stages in screw-based configurations and compressive pre-shearing stress is induced while making the connection between loading piston and specimen in vacuum-based configurations. In order to overcome these technical problems, a special auto compensation system was incorporated into an existing cyclic triaxial apparatus, allowing: (1) no physical contact between loading piston and specimen to achieve an isotropic consolidation state, (2) the later connection between these two components to be easily accomplished with almost insignificant disturbance on the specimen (maximum 100 N in axial force). To assess the performance of this auto compensation system, two experiments of same dense reference sand specimens were respectively conducted, and the results were found to be similar, showing the good repeatability. Moreover, as compared with screw-based configuration, the test specimen did not undergo an adverse tensile pre-shearing. As a result, the test specimen became more resistant to cyclic mobility. On the contrary, as compared with another vacuum-based configuration (without auto compensation) well-documented in the literature, the obtained result was less stable since the employment of auto compensation system ensured that there was no beneficial compressive pre-shearing during the connection stage. The results obtained in this study showed the good performance of the developed auto compensation system in the triaxial test apparatus for liquefaction analysis.

Investigation of physical and mechanical properties of mortars produced by polymer coated perlite aggregate

With its low unit weight, expanded perlite (EP) offers significant advantages in heat and sound insulation in the construction sector. However, due to its high-water absorption capacity, EP affects the physical and mechanical properties of concrete negatively. Therefore, it is aimed to reduce water absorption by coating the EP with polymer and thus to improve its mechanical and physical properties. In this study, mortar production was carried out by replacing coated and uncoated EP with CEN reference sand at 0%, 20%, 40%, 60%, and 80% respectively. The effective water/cement ratio of all produced mortar samples was determined to be 0.6. For coated and uncoated EP aggregate mortar series, unit weight, compressive strength, bending tensile strength, water absorption, ultrasonic pulse velocity (UPV), and thermal conductivity coefficient were determined. The results showed that the unit weight of the mortar samples decreased as the amount of EP increased, but their physical and mechanical properties also changed. Mortar samples with better thermal insulation properties were obtained with decreasing thermal conductivity values. The polymer coating of EP improved physical and mechanical properties. Especially in the 80% substituted EP series, the thermal conductivity decreased from 1.20 to a coefficient of 0.91 W/mK.

Fresh and hardened properties of self-compacting mortar containing limestone as fine aggregates

An experimental attempt was presented in this work to reduce the weight of self-compacting concrete by replacing sand entirely with limestone. Therefore, three mixes were prepared, and the same constituent materials were used in these mixes, excluding the fine aggregate type. In the reference mix, conventional sand was employed, but the sand was entirely eliminated and replaced with limestone in the other two. One mix contained untreated limestone, while the remaining was with limestone treated by immersing in the alkaline solution for 24 h. The mixes were contrasted in the fresh and hardened cases. In a fresh situation, the mixes with both limestones' forms were less workable than the reference mix. In hardened case, the sand replacement with limestone reduced the mixes' weight, about 10.9–11.3%. According to the compressive and flexural strengths, the mixes with limestone showed different findings. While the untreated mix gave the smallest strengths, the mix with treated limestone exhibited the most significant enhancement in compressive and flexural strength, where it recorded strengths larger than the reference sand mix.

N immobilization treatment revisited: A retarded and temporary effect unfolded in old‐field restoration

AbstractAimThere is increasing recognition that plant–soil feedbacks drive species co‐existence; therefore the below‐ground compartment should be better considered in ecological restoration. Addition of carbon is a restoration measure that relies on indirect plant–soil relationships by immobilizing soil nitrogen in microbial biomass to manipulate competitive hierarchies between plant species. The aim of the present work was to evaluate the impact of six years of carbon amendment in old‐field restoration in the long term, 20 years after the first application.LocationOld‐fields and reference sand steppe on dry calcareous sandy soil in Fülöpháza, Kiskun LTER site (46°53′ N, 19°24′ E), Hungary, Pannonian biogeographic region, Europe.MethodsWe applied carbon amendment in the form of sucrose and sawdust on three abandoned agricultural fields between 1998 and 2003. Vegetation was surveyed in 1998–2006 and re‐sampled in 2008, 2010 and 2018 on permanent 2 m × 2 m coenological relevés for carbon‐amended, control and reference plots (n = 144). We used principal response curves (PRC) to describe vegetation development trajectories and linear mixed‐effects models to test changes in cover of vascular plants and cryptogams, nitrogen requirement groups and restoration species groups with time and treatment.ResultsCarbon amendment resulted in lower soil nitrogen availability, and lower cover of vascular plants and cryptogams compared to control, but these differences became visible only four to five years after the first application and disappeared three years after the cessation of treatment. Minor treatment effects on the cover of oligotrophic, mesotrophic and target species were found.ConclusionsCarbon amendment did not speed up the recovery of sand grasslands; however, the reduction of cover (vegetation and cryptogam) can be a window of opportunity for other species to colonize that can be used as a complement to other treatments. Long‐term monitoring is especially important in evaluating restoration interventions that focus on indirect above‐ground–below‐ground linkages.

Determination of damping ratio using Monte-Carlo method

This paper highlights an innovant method for calculating the damping ratio using Monte-Carlo method. Compared with other approaches reported in the literature, the clear benefit of the method is the ability to directly determinate the damping ratio upon irregular stress-stain curves through Python. By using Monte-Carlo method, it is found that (i) the computed damping ratios are consistent with the undrained cyclic triaxial result on a dense reference sand specimen; (ii) while total random samplings number for each hysteresis loop greater than 5000 times, the method could provide a satisfactory analysis.

Evaluation of Electrostatic Separation of Microplastics From Mineral-Rich Environmental Samples

Reliable, easy, cost-effective and reproducible ways of extracting microplastics (MP) from environmental samples remains an important requirement for MP research. In this context, electrostatic separation is a new proposition, especially for extracting MP from mineral-rich samples and large sample volumes. However, there is little research evaluating the reliability of the technique. This study has evaluated the effectiveness of the Korona-Walzen-Scheider (KWS) system; a small-scale version of larger machines designed to sort recycling materials. Recovery rates of a variety of sizes of MP, spiked in beach sediments, were found to be highly dependent on the MP size. MP ≥ 2 mm achieved 99 - 100% recovery (with the exception of fibres: ~80%), MP of 63 – 450 µm achieved ~60 – 95% recovery and MP of 20 µm achieved ~ 45% recovery. For particle-based analysis, additional density separation is still inevitable for the analysis of small MP after KWS separation and further reduces the overall recovery rates. Mass reduction rates of beach and commercial reference sand greatly differed, 93% and 17%, respectively. Mineral analysis using SEM-EDX suggested that lower reduction rates found in commercial sand was due to high presence of small ( 450 µm, electrostatic separation is a reliable and fast approach for MP extraction from the environment.

Evaluation of Diffusivity and Wettability of Crude Oil-Contaminated Sand from Offshore Petroleum Facility Prior to Remediation Process

Cleansing of crude oil-contaminated sand is anticipated to rely heavily on the ability of cleaning solution to access the contamination sites and the bonding strength between crude oil and sand. In this research, the actual produced sand sample from an oilfield and reference sand sample taken from a beach were subjected to porosity, permeability, and wettability tests. Results revealed that the particle size of the sands dominated the porosity and permeability outcomes. While the porosity of the reference sand at 46.64% was barely higher than the produced sand, the permeability (in Darcy) of the former exceeded the latter by 10 folds. In wettability and interfacial study, the highest adhesion strengths at the oil-sand interface were calculated according to Young-Dupre equation. The computed values were 58.42 mN/m for the reference sand and 65.88 mN/m for the produced sand, assuming 3-species geometric-mean model from Owen/Wendt theory. The types of intermolecular bonding at the interface were dispersive (London dispersion force from Van der Waals bonding), dipole-induced dipole attraction and mechanical adhesions, justifiable through elementary analysis. All the findings including corroboration from thermogravimetric analysis suggest that relatively higher energy was required to remediate the produced sand from oil reservoir as compared to the reference sand retrieved from shoreline.

DEF damage in heat cured mortars made of recycled concrete sand aggregate

The purpose of this study is to investigate DEF development in heat cured mortars made of recycled sand aggregate with sodium sulphate or gypsum plaster powder additions to stimulated DEF development. Ten different formulations have been studied for more than a year. DEF damage comparison between different mortars made of RCA sand and standardised siliceous sand is made with or without sulphate addition. Sodium sulphate was used in three formulations at 5% of total SO3 by cement weight, while gypsum plaster powder was used in four formulations with two different fineness (<0.1 mm and 0.1–2 mm) and contents (1.2% and 0.8% of sulphate content in sand) to simulate a scenario of recycled aggregate pollution by gypsum plaster during the demolition phase. Three other mortars were formulated without any addition to determine the impact of sulphate addition. Sodium sulphate was found to induce and amplify DEF. Gypsum plaster powder did not enhance damage and both mortars made of recycled sand with or without gypsum addition showed little differences concerning DEF expansion. RCA based mortars had lower DEF damage than siliceous reference sand based mortars. This result is explained by air entrainment effect of RCA sands and to a lesser extent by chemical differences between mortars made of recycled and siliceous sand. Hence, DEF damage should be further studied at sulphate and alkaline content far above the current standard limits for RCA based concretes.

Influence of Exposure to Elevated Temperatures on the Physical and Mechanical Properties of Cementitious Thermal Mortars

Thermal mortars incorporating insulating aggregates are a possible solution to ensure good thermal performance and thermal comfort in buildings due to their low thermal conductivity coefficient. Under some circumstances, namely for particular in-service conditions in industrial applications and/or accidental actions (such as fire), it is important to quantify the retention of their properties after exposure to elevated temperatures, however this information is not yet available in the literature. This study aims to characterize the physical and mechanical behavior of thermal mortars incorporating expanded clay, granulated expanded cork and silica aerogel as aggregates after exposure to elevated temperatures. To this end, five types of mortars were produced in laboratory conditions—three thermal mortars, one reference sand mortar and one sand mortar with admixtures—and then exposed to different elevated temperatures (from 20 °C to 250 °C) in a thermal chamber. After thermal exposure, the following properties were assessed: bulk density; ultrasonic pulse velocity; dynamic elasticity modulus; dynamic shear modulus; Poisson coefficient; compressive strength; and thermal conductivity. The results obtained show that residual properties present a very high dependence on the reactions that take place in the cement paste when the mortars are exposed to elevated temperatures. After such exposure, all mortars with thermal insulating aggregates were able to maintain their insulating characteristics, but experienced internal damage and degradation of their mechanical properties. Results obtained also showed that insulating aggregates allowed to produce mortars with higher aggregate-cement paste compatibility at elevated temperatures compared to conventional mortars, resulting in less micro-cracking of the mortar, and leading to lower reductions in thermal conductivity with increasing temperature.

Environmental remediation of synthetic leachate produced from sanitary landfills using low-cost composite sorbent

Abstract The possibility of preparing a composite sorbent consisted of an activated carbon (AC) and waste foundry sand (WFS) for the treatment of synthetic leachate is of greater importance in this work; particularly the use of byproduct waste as a substitute for commercial material. A composite sorbent of 25% activated carbon mixed with 75% waste sand was able to remove the dissolved organic constituents (DOC), ammonia nitrogen (NH3-N) and the divalent dissolved zinc ions (Zn(II)) from simulated leachate in the acetogenic and methanogenic phases with removal efficiencies not less than 75%. For column tests, two beds were prepared from mixing of composite sorbent and reference sand (which consisted of 40% fine sand and 60% coarse sand) with weight proportions of 10:90 and 20:80 to obtain acceptable hydraulic conductivity and reactivity. For leachate with two phases under consideration, the increase of composite sorbent from 10 to 20% will increase the capturing of contaminants and longevity of the barrier for same location along the packed bed; however, this was associated with slight decrease of hydraulic conductivity. Empirical models such as those depicted by Thomas, Belter and Yan have yielded satisfactorily agreement for the uptake of DOC, NH3-N and Zn(II) multicomponent of the simulated leachate through the mentioned beds with determination coefficient ≥ 0.959, Nash–Sutcliffe efficiency ≥ 0.98, and sum of squared errors ≤ 0.78.

Parameter Evaluation of Exponential-Form Critical State Line of a State-Dependent Sand Constitutive Model

In sand constitutive models, it is of cardinal importance to consider a state parameter to distinguish the real dilatancy for cohesionless soils (sand), which is different from cohesive soils (clay). Thus, one of the key issues in simulating the sand behaviour is the better representation and parameter calibration of critical state line (CSL) for estimating contraction in loose state and dilatancy in dense state, respectively. For this purpose, a new exponential form for CSL with two model constants a and b has been presented in the literature. This paper provides a valuable insight into the two model constants, controlling the shape of the critical state line by simulating a uniform quartz reference sand (Hostun RF) in loose and dense states under undrained triaxial conditions. It can be concluded that the liquefaction behaviour in loose state is fundamentally affected by even a minor variation in model constant a , but insensitive to model constant b . Moreover, the linear fitting calibration of CSL recommended in the literature is complicated in consideration of the non-unified critical state line. Thus, the maximum void ratio in the natural state could be considered as a comparison basis on which to evaluate the liquefaction potential as an alternative. The numerical results showed good agreement with real experimental data. However, in dense state, the dilatant behaviour of sand was found to be mainly controlled by model parameter b . In addition, the influence of a non-unified critical state under various confining pressures on the determination of b should not be neglected. With the correction of b , the numerical results were found to be consistent with the experimental data concerning Hostun RF sand.